Cationic Aluminum Alkyl Complexes Incorporating Aminotroponiminate Ligands

The synthesis, structures, and reactivity of cationic aluminum complexes containing the N,N‘-diisopropylaminotroponiminate ligand (iPr2-ATI-) are described. The reaction of (iPr2-ATI)AlR2 (1a−e,g,h; = H (a), Me (b), Et (c), Pr (d), iBu (e), Cy (g), CH2Ph (h)) with [Ph3C][B(C6F5)4] yields (iPr2-ATI)AlR+ whose fate depends on the properties of the R ligand. 1a and 1b react with 0.5 equiv of [Ph3C][B(C6F5)4] to produce dinuclear monocationic complexes [{(iPr2-ATI)AlR}2(μ-R)][(C6F5)4] (2a,b). The cation 2b contains two (iPr2-ATI)AlMe+ units linked by an almost linear Al−Me−Al bridge; 2a is presumed to an analogous structure. 2b does not react further with [Ph3C][B(C6F5)4]. However, 1a reacts with 1 equiv [Ph3C][B(C6F5)4] to afford (iPr2-ATI)Al(C6F5)(μ-H)2B(C6F5)2 (3) and other products, presumably via C6F5- and ligand redistribution of a [(iPr2-ATI)AlH][(C6F5)4] intermediate. 1c−e react with 1 equiv of [Ph3C][B(C6F5)4] to yield stable base-free [(iPr2-ATI)AlR][B(C6F5)4] complexes (4c−e). 4c crystallizes from as 4c(ClPh)·0.5PhCl, which has been characterized by X-ray crystallography. In the solid state PhCl ligand of 4c(ClPh) is coordinated by a dative PhCl−Al bond and an ATI/Ph π-stacking interaction.1g,h react with [Ph3C][B(C6F5)4] to yield (iPr2-ATI)Al(R)(C6F5) (5g,h) via C6F5- transfer of [(iPr2-ATI)AlR][(BC6F5)4] intermediates. 1c,h react with B(C6F5)3 to yield (iPr2-ATI)Al(R)(C6F5) (5c,h) via C6F5- transfer of[(iPr2-ATI)AlR][RB(C6F5)3] intermediates. The reaction of 4c−e with MeCN or acetone yields [(iPr2-ATI)Al(R)(L)][B(C6F5)4] adducts (L = MeCN (8c−e), acetone (9c−e)), which undergo associative intermolecular exchange. 9c−e undergo slow β-H transfer to afford the dinuclear dicationic alkoxide complex [{(iPr2-ATI)Al(μ-OiPr)}2][B(C6F5)4]2 (10) and the corresponding olefin. 4c−e catalyze the head-to-tail dimerization tert-butyl acetylene by an insertion/σ-bond metathesis mechanism involving [(iPr2-ATI)Al(C⋮CtBu)][B(C6F5)4] (13) and [(iPr2-ATI)Al(CHC(tBu)C⋮CtBu)][B(C6F5)4] (14) intermediates. 13 crystallizes as the dicationic complex [{(iPr2-ATI)Al(μ-C⋮CtBu)}2][B(C6F5)4]2·5PhCl from chlorobenzene. 4e catalyzes polymerization of propylene oxide and 2a catalyzes the polymerization of methyl methacrylate. 4c,e react ethylene-d4 by β-H transfer to yield [(iPr2-ATI)AlCD2CD2H][B(C6F5)4] initially. Polyethylene is also in these reactions by an unidentified active species.